A dad died of a massive caffeine overdose after eating mints bought from his local sweet shop – not knowing they were laden with the stimulant.

John Jackson, 40, was found dead by relatives at his West Midlands flat after eating from a £4 packet of Hero Instant Energy Mints. Just one of the sweets is said to contain more caffeine than a whole can of a high-energy drink, like Red Bull.

At an inquest in Smethwick on Thursday, coroner Robin Balmain said he would be writing to the Department of Health demanding answers over the death of the former painter and decorator.

He said: ‘‘This is a potentially very dangerous situation. The level of caffeine is enormous. I think it’s as certain as I can be that Mr Jackson didn’t know that he was going to expose himself to this sort of danger.”

Mr Jackson was found dead by his estranged partner and stepdaughter at his flat in Walsall Road, Darlaston on May 2.

The UK-produced mints are sold alongside other sweets, but shocked makers last night stressed they had taken a series of measures to warn about the high caffeine content.

A post mortem showed Mr Jackson had 155mg of caffeine per litre of blood in his system, yet just 10mg would have been considered an overdose, according to pathologist Dr Dragana Cvijan.

She told the inquest: “The most important compound found in the post mortem was caffeine. I must say this is the first time in my experience that I’ve come across a caffeine overdose.”

She gave the medical cause of death as caffeine toxicity but said Mr Jackson, a heavy drinker, also had cirrhosis of the liver which had played a part in the tragedy, leaving him unable to absorb the stimulant properly.

Miss Court, 23, said: “On the box they said one tablet equals one can of energy drinks. A kid could go in and buy them and the same thing could happen to him.”

Mr Balmain, ruling that death was due to an accident, said: “I’m also going to write to the Department of Health because coroners have got powers under recent legislation to draw the attention of appropriate authorities to things that might be a danger to other people.

“I didn’t know about these sweets, and if it’s the equivalent to Red Bull, you can’t imagine people drinking dozens and dozens of cans of Red Bull.’’

Miss Court, who was joined at the hearing by sister Amanda said afterwards: “It’s unbelievable – never in the world would I have thought it was caffeine, to be fair. I would have thought it was alcoholic liver disease that killed him. I think there should be something done about them [the mints]. They are very, very dangerous.

“They are classed in the same place as Polos and Extra Strong Mints. I’m scared to drink coffee now and I don’t get anything with caffeine in it.”

Amanda, 27, added: “My daughter is eight. If she was going to go in and buy them she wouldn’t think they were going to harm her.”

The pair added their stepfather did not drink coffee or tea and only occasionally consumed Coca Cola, other key sources of caffeine.

Last night a statement was issued by directors of the Birkenhead company behind the mints, Hero Energy Ltd.

Paul Hayes and Steve Hones said they were ‘‘shocked and deeply concerned’’ at the tragic death.

Their statement read: "Both myself and HERO co-founder, Steve, are greatly shocked by this news and are deeply concerned.

"Firstly, all of our thoughts and condolences go to Mr Jackson's family and friends. This is terrible news and something no one should have to go through.

"Here at HERO, we fully understand the associated risk and dangerous of caffeine and its consumption. We are extremely vocal about these risks and highlight them at every available opportunity. Our customers health and safety is the most important thing to us and we thus already action the below:

Clear writing on each tin stating they contain caffeine. We also have a clear warning stating "WARNING: CONTAINS HIGH LEVELS OF CAFFEINE. Not recommended for pregnant women, children under 16 & caffeine sensitive individuals. DO NOT exceed 5 HERO Mints in a 24 hour period."

Clear writing on the shelf display pack stating the same as the tin: "WARNING: CONTAINS HIGH LEVELS OF CAFFEINE. Not recommended for pregnant women, children under 16 & caffeine sensitive individuals. DO NOT exceed 5 HERO Mints in a 24 hour period."

The website has an entire page dedicated to responsible use of caffeine, going into great detail, and can be found here: http://heroenergy.co.uk/responsible-use

We produce our mints, and pack them, with pharmaceutical grade companies to make sure they are safe and to the highest qualtiy. We would not settle with a standard candy/mint producer.

We also add additional attributes to our mints to stop consumers eating too many in one sitting. These include:

There are high levels on menthol in each mint (much like a Fisherman's Friend) to put people off eating many of them at once.

They are priced at an extreme premium to put people off from buying many tins at once.

The bitterness of the caffeine comes through the mint to make sure consumer realise they are more than just a mint.

The effect of the caffeine is very quick so after even just one mint you realise it.

Making sure children under 16 do not abuse caffeine is something that is particularly important to us. We believe children of this age do not need caffeine stimulants and we are currently formulating a plan to take this further in the UK.

The levels you have mentioned would have meant Mr Jackson must have consumed over 300 of our mints, which is staggering. After 5 mints, over a 24 hour, period most people would find it difficult to consume anymore.

We are still a relatively young business (formed in 2011) and this is the first major incident we have heard of in relation to our product.

All this being said, we are very saddened by the news and will immediately look into how we can further make our consumers aware of the risks of caffeinated products."